Can't smearing be switched off?

[peter_deak1]

Dear Experts,

recently I came across a defect in silicon, which has two stable states, depending on the occupation of the two nearly degenerate defect levels. I tried to switch of occupation smearing by setting SIGMA = 0.0 (with ISMEAR = 0 or -1), to get only one state occupied with one electron (instead of both nearly half-and-half), but it did not seem to work. Finally I've managed with prescribed occupation (FERWE, FERDO), but is there a way to switch off smearing without that? (I'm using VASP 5.4.4.)

Best regards

Peter Deák

[martin.schlipf]

If you use the tetrahedron method there is no smearing, so it should be able to find the correct occupancies even for very small gaps. A very small smearing should also work, but SIGMA = 0 has a special meaning and is used for fixed occupancies. The relevant threshold is 1e-5 so anything smaller than that will not work as intended.